There exist a variety of wireless systems which, illustratively, are used for short range distance communication. Some systems are used for communication around the human body; other systems may be used for communication in or around other objects. For example, currently RF based hearing aids are considered for wireless communication. Often such hearing aid systems operate in the 2.5 GHz ISM band. Such systems feature propagation by means of transverse waves, the magnetic and electric fields being in phase and covering a relatively large range of perhaps 30 meters. The large range may cause problems in terms of security of the communication content and may cause interference. Furthermore, because of their relatively high frequency of operation, such systems are heavily influenced by the human body.
Somewhat more conventional hearing aids employ magnetic field induction as a wireless communication method. Unfortunately, magnetic field induction based wireless systems have a limited range if the antenna is comparatively small, such as would be required in a hearing aid. Not all parts of the human body can be reached with magnetic field induction-based systems with small antennas. Consequently, it can be difficult to provide communication between a hearing aid and a hand-held control using such systems.
FIG. 1 is a circuit diagram of a prior art wireless communication system utilizing magnetic field induction. Reference numeral 11 denotes a transmitter which may illustratively be contained in a hearing aid designed for positioning proximate to or into one ear. Reference numeral 13 denotes a receiver which may illustratively be contained in a hearing aid designed for positioning proximate to or into the other ear. It is desired to have communication between the two hearing aids so that signals transmitted from transmitter 11 and received by receiver 13 may be processed (by processing circuitry near or inside the receiver) to enhance the user's hearing experience and make that experience more natural. In certain implementations, bidirectional communication is also possible in which transmitter 11 and receiver 13 are transceivers. Transmitter 11 contains sources 25 and 27 and a resonant circuit which includes coil 15 and capacitor 19. Magnetic field 291, also denoted as H1, is generated via coil 15. Receiver 13 contains a resonant circuit formed by coil 17 and capacitor 21 and a low noise amplifier 23. The resonant circuit of receiver 13 resonates at the same frequency as the resonant circuit of transmitter 11. A voltage is induced in coil 17 by magnetic field 292, also denoted as H2, thereby creating a signal communication path. The mutual coupling factor between coils 15 and 17 is denoted by M, reference numeral 41.